Physicists are accelerating the hunt for revolutionary artificial atoms

Scientists at the University of Bath have taken an important step towards understanding the interaction between layers of atomic thin materials arranged in stacks. They hope that their research will accelerate the discovery of new, artificial materials, and lead to the design of electronic components that are far thinner and more efficient than what is known today.

Smaller is always better in the world of electronic circuits, but there’s a limit to how far you can shrink a silicon component without it overheating and falling apart, and we’re close to achieving that. The researchers are investigating a group of atom-thin materials that can be assembled into stacks. The properties of each final material depend both on the choice of raw materials and on the angle at which one layer is arranged on top of the other.

Dr Marcin Mucha-Kruczynski, who led the study in the Department of Physics, said: “We have found a way to determine how strong atoms are in different layers of a stack, and we have demonstrated the application of our idea for a structure made of graphene layers. “

The Bath Research, published in Nature communication, is based on earlier works on graphene – a crystal characterized by thin sheets of carbon atoms arranged in a honeycomb design. In 2018, scientists at the Massachusetts Institute of Technology (MIT) found that when two layers of graphene are stacked and then twisted relative to each other by the ‘magic’ angle of 1.1 °, they produce a material with superconducting properties. This was the first time that scientists made a super-conductive material made purely from carbon. However, these properties disappeared with the slightest change of angle between the two layers of graphene.

Since the MIT discovery, scientists around the world have been trying to apply this ‘stacking and twisting’ phenomenon to other ultra-thin materials, allowing two or more atomic different structures to be placed together in the hope of forming completely new materials. with special qualities.

“In nature, you can’t find materials where each atomic layer is different,” said Drs. Mucha-Kruczynski. “What’s more, two materials can normally only be assembled in one specific way, because chemical bonds must form between layers. But for materials like graphene, only the chemical bonds between atoms on the same plane are strong. The forces between planes – known as van der Waals interactions – are weak, and this makes it possible to twist layers of material with respect for each other. “

The challenge for scientists now is to make the process of discovering new, layered materials as efficient as possible. By finding a formula by which they can predict the outcome when two or more materials are stacked, they will be able to streamline their research enormously.

It is in this area that Dr Mucha-Kruczynski and his collaborators at the University of Oxford, Peking University and ELETTRA Synchrotron in Italy expect to make a difference.

“The number of combinations of materials and the number of angles at which they can be twisted is too large to try out in the lab, so what we can predict is important,” said Drs. Mucha-Kruczynski.

The researchers have shown that the interaction between two layers can be determined by studying a three-layer structure where two layers are composed as you might find in nature, while the third is distorted. They used angle-resolved photoemissyspectroscopy – a process in which powerful light emits electrons from the sample so that the energy and momentum from the electrons can be measured, giving insight into the properties of the material – to determine how strong two carbon atoms are in a given distance from each other are linked. They have also shown that their result can be used to predict properties of other stacks made of the same layers, even if the turns between layers are different.

The list of known atomic thin materials like graphene is growing all the time. It already contains dozens of inputs that display a wide range of properties, from isolation to superconductivity, transparency to optical activity, brightness to flexibility. The latest discovery provides a method for experimental determination of the interaction between layers of any of these materials. This is essential for predicting the properties of complex stacks and for the efficient design of new devices.

Dr. Mucha-Kruczynski believes it may be 10 years before new stacked and twisted materials find a practical, everyday application. “It has taken a decade for graphene to move from the laboratory to something useful in the ordinary sense, so with a hint of optimism, I expect a similar timeline will apply to new materials,” he said.

Building on the results of his latest study, Dr. Mucha-Kruczynski and his team now work on twisted stacks made of layers of metal dichalkogenides (a large group of materials with two very different types of atoms – a metal and a chalcogen, such as sulfur). Some of these stacks have shown fascinating electronic behavior that scientists are not yet able to explain.

“Because we are dealing with two radically different materials, studying these stacks is complicated,” explained Dr. Mucha-Kruczynski. “However, we are hopeful that over time we can predict the properties of various stacks, and design new multifunctional materials.”